1. Field of the Invention
The present invention generally relates to a fuel cell system and a method of controlling the fuel cell system. More particularly, the present invention relates to a fuel cell system and a method of controlling the same, which dilute emitted hydrogen using a bypass valve disposed between a bypass passage and a passage at an inlet of a fuel cell stack.
2. Description of the Related Art
A fuel cell vehicle includes a fuel cell stack with laminated multiple fuel cells that are used as a power source; a fuel supply system configured to supply hydrogen as a fuel for the fuel cell stack; an air supply system configured to supply oxygen as an oxidant necessary for electrochemical reactions; and a water and heat management system configured to adjust temperature of the fuel cell stack. The fuel supply system decompresses compressed hydrogen within a hydrogen tank and supplies the decompressed hydrogen to a fuel electrode (anode) of the stack. The air supply system is configured to supply air suctioned from exterior using an air blower to an air electrode (cathode) of the stack.
When hydrogen and air are provided to the fuel electrode and air electrode of the stack, respectively, hydrogen ions are extracted through a catalysis reaction at the fuel electrode. The separated hydrogen ions are delivered to the anode through an electrolyte membrane, and the hydrogen ions and electrons from the fuel electrode produce an electrochemical reaction with oxygen to generate electric energy at the anode. Specifically, an electrochemical oxidation of hydrogen at the fuel electrode and electrochemical reduction of oxygen at the air electrode induces the electrons to move, and moving of the electrons generates electricity and heat. Additionally, water vapor or water is generated by the chemical action of combining hydrogen with oxygen.
An emission device is configured to emit unreacted hydrogen and oxygen, and by-products generated during the electric energy generation including water vapor, water, and heat. Further, gases such as water vapor, hydrogen, and oxygen are emitted to the air through a ventilation hood. Regarding emissions, to satisfy environmental standards, hydrogen should be emitted after being diluted with air. Accordingly, a method for decreasing the amount of hydrogen when an ignition of a fuel cell vehicle is turned off has been disclosed. However, as according to this method of the related art, the durability of a fuel cell stack may be damaged and thus, a method for diluting hydrogen with air supplied from an air supply system of the fuel cell system is required.